Smooth pursuit was defective in four patients with congenital nystagmus. However the likely cause of congenital nystagmus in these patients was related to a defect in orbital position integration. None of the three patients with congenital nystagmus demonstrated improvement following administration of L-5-hyroxytryptophan. One patient with acquired periodic alternating nystagmus (PAN) responded to Baclofen with suppression of the nystagmus and improvement in vision. One of the patients with congenital PAN did not respond. One patient with irregular nystagmus has been identified to have the diencephalic syndrome.